Question: Simplify the following expression: $t = \dfrac{1}{8y} - \dfrac{1}{5y}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $8y$ and $5y$ $\lcm(8y, 5y) = 40y$ $ t = \dfrac{5}{5} \cdot \dfrac{1}{8y} - \dfrac{8}{8} \cdot \dfrac{1}{5y} $ $t = \dfrac{5}{40y} - \dfrac{8}{40y}$ $t = \dfrac{5 -8}{40y}$ $t = \dfrac{-3}{40y}$